Ad a coupon (gift certificate) without shipping

Hi
We have a system, selling membercards and gift certificates (or vouchers) with HIKA shop.
The membercards we send by post and for that we need a shipping method.

One possibility ist that somebody recieves a gift certificate (that someone other buys for him and got a code).
The user who purchases the membercard in the shop with the gift certificate (coupon), don't have to pay the shipping amount.

Now, i had the idea to create another product for that with another weight. Then i define in the shipping method, that all products with a weight between x and y don't have a adsitional shipping amount. So far it's OK, but:

All User could order this product without shipping amount, even though I descibe in the product, that it is only for users with coupon code.
How I can handle it, that a user with a coupon code (gift certificate) had to put in first the code and then he would see this additional product?
Can I hide products for all User, they don't have a valid coupon code?

Hi,

You can't have hidden products which would display based on a coupon code.
I don't know of any extension which would be able to handle that.

It would require a customization by a developer I'm afraid.

OK, but can I stop the user and prohibit the next step in the Checkout, if the Code is incorrect?
Is it possible, give the user a message, if the Code is correct given?
Thank you

You can remove the "next" button if their is no coupon code.
For that, edit the file "cart" of the view "checkout" via the menu Display->Views and at the beginning you can add:
<?php
if(empty($this->coupon)){
$this->nextButton=false;
}else{
echo 'the code given is correct';
}
?>